1. Field of the Invention
The present invention relates to the display of measured parameters generally and, more particularly, but not by way of limitation, to novel compact, low-cost, semiconductor device and methods for receiving arbitrary input parameters and driving selected display devices and methods therefor, which are particularly useful in motorized vehicles.
2. Background Art
Particularly in motorized vehicles, but not necessarily limited thereto, there is need for measuring and displaying physical parameters such as pressure, temperature, liquid level, voltage, and current and, in some cases, providing high and/or low indications thereof. Conventionally, almost all of these functions are satisfied by various electromechanical gauges which are relatively expensive and space-consuming. When high and/or low indication is required, auxiliary sensors and displays are frequently employed, as it is more economical to do so rather than derive the presence of an extreme condition from the normal measurement signal. Also, in order to accommodate the electromechanical display devices, the sensors must often be designed to be very non-linear, since the amount of freedom to shape the display device is quite limited. This latter factor introduces additional cost and space consumption to conventional systems.
It would be desirable to have a method and apparatus for physical parameter measurement and display which is particularly well suited for parameters such as pressure, temperature, liquid level, voltage, and current. There exists a wealth of inexpensive sensors and transducers which can provide electrical inputs to such a device. Unfortunately these transducers and sensors come in a very large number of electrical forms and non-linearities. It is, therefore, a first objective of the present invention to accept an arbitrary shape and, to some extent, arbitrary amplitude input signal.
It is very often desirable to contour the displayed information in order to shape, compress, or expand the parameter for ergonomic or resolution reasons. It is, therefore, a second objective of the invention to display the parameter in an arbitrary shape.
Many of the available inexpensive transducers and sensors have rather low impedances, requiring an excessive amount of power (in the context of the "micro-instrument" provided by the present invention). It is, therefore, a third objective of the invention to operate the mating transducer in one of several power conserving modes.
Some transducers are designed to provide an increasing output for an increasing physical parameter while others produce a decreasing output for an increasing input. It is, therefore, a fourth objective of the invention to treat the input in a normal (ascending) mode or an inverted (descending) mode.
In some cases the input signal comes from a calibrated source (e.g., absolute volts), but in other cases the input signal comes from a transducer which must be excited by the device (frequently in a power conserving mode). It is, therefore, a fifth objective of the invention to operate in either an "absolute" or "ratio" mode.
Some parameters are inherently jittery, or noisy (such as a fuel sender in a sloshing tank). It is, therefore, a sixth objective of the invention to provide varying degrees of damping or slew rate control. For example, relatively fast for pressure and voltage, or relatively slow for fuel level and temperature.
In critical applications, a second sensor is frequently introduced, as noted above, to warn or shut down an operation when an out-of-specification condition is detected. It is a seventh objective of the invention to provide a programmable over and/or under warning output.
In other critical applications, both a second and third sensor may be introduced to warn and/or shut down an operation when either a low or high out-of-specification condition is detected. It is, therefore, an eighth objective of this device to provide at least one additional programmable over and/or under warning output.
Most instruments designed for the vehicle market incorporate illumination. It is, therefore, a ninth objective of the invention to provide self-illumination by directly driving light-emitting diodes.
The light emitting diodes may be illuminated sequentially (pointer mode) or additively (bar graph mode). It is, therefore, a tenth objective of the invention to provide self-illumination in either of two modes, pointer or bar graph.
In some applications, such as portable battery operated equipment, it becomes necessary to run the device and transducer at very low power levels. It is anticipated that an inherently low power (or high impedance) transducer will be operated in one of the power conserving modes, and that the device will be operated in a direct drive LCD mode. In this mode a liquid crystal display may be driven without the need for temperature compensation over the temperature range of -40 degree C. to +85 degree C. It is, therefore, an eleventh objective of the invention to directly drive a liquid crystal display.
The LCD may be activated sequentially (pointer mode) or additively (bar graph mode). It is, therefore, a twelfth objective of the invention to provide low power LCD activation in either of two modes, pointer or bar graph.
Both the LED and LCD Display drives address individual segments. These segments may be arranged in limitless configurations; straight line vertical, straight line horizontal, straight line diagonal, curved up, curved down, patterns, matrices, etc. Two or more light emitting diodes can be simultaneously energized in series. Two or more LCD segments can be simultaneously energized in parallel. Static light emitting diodes can be energized directly, but static LCD segments require an AC drive signal. The static elements are envisaged as part of the scale legend or information, and are intended to be active whenever the power is applied. It is, therefore, a thirteenth objective of the invention to provide a continuously operating LCD segment driver.
The light emitting diodes can be assembled in specific color coded formats. For example, the traditional OK-Caution-Warning/Stop sequence of Green-Yellow-Red can be arranged within the display to impart that interpretation, while simultaneously "pointing" to the measured value. When coupled with scale expansion and contraction contouring the display can impart an unusually large amount of accurate information with relatively few display elements. It is, therefore, a fourteenth objective of the invention to provide color coded status information integral with the measurement.
When an out-of-specification condition is detected, it is often desirable to "flash" the display to draw attention to the fact that a problem exists. It is, therefore, a fifteenth objective of the invention to provide various flashing modes at the upper limits of the range or the lower limits of the range.
If an out-of-specification condition can occur at both extremes of the range, it may be desirable to "flash" the display for both conditions. It is, therefore, a sixteenth objective of the invention to provide various independent flashing modes at both the upper limits of the range and the lower limits of the range.
When information is known to vary at a slow rate, it may be desirable to limit the update of the display to rather long intervals to reduce apparent "flicker" when a borderline reading is made in a noisy environment. It is, therefore, a seventeenth objective of the invention to provide various conversion rate intervals. This will usually be used in conjunction with the slew rate control (objective six).
When information is known to be somewhat noisy, it may be desirable to introduce hysteresis to lessen the likelihood of borderline flicker. It is, therefore, an eighteenth objective of the invention to provide an hysteresis on/off feature. This will usually be used in conjunction with the conversion rate control (objective seventeen) and the slew rate control (objective six).
Having separate control over slew rate, conversion rate, and hysteresis allows for a large number of possibilities in solving the jitter and noise problems in systems with various response time requirements. Taken together they allow for ergonomic fine-tuning relative to the display, and/or warning response fine-tuning relative to the output signals.
The method and apparatus described herein has been architecturally optimized for a singe chip triple technology implementation (triple tech=analog, digital, and non-volatile memory in complementary MOS), on a particularly small and inexpensive die. The solution for the complete instrument must be cost competitive with the optimized evolved electromechanical gauges and their one hundred year market domination. It is, therefore, a nineteenth objective of the invention to be substantially integratable in a small, inexpensive, triple technology chip.
It is intended that one and only one chip serve all the instrumentation needs of a product line that will operate from numerous power sources, with innumerable transducers, displaying numerous transforms in either LED or LCD formats, with many functional options. Therefore, it is desirable that the invention will be programmable at the chip level via non-volatile memory, and at the circuit board level via "stuffing" instructions. Typical stuffing instructions will be resistor values for voltage options. Resistor values for classes of transducers, capacitor values for filter response, LED arrays for specific color formats, LCD assemblies for specific legend, etc. It is, therefore, a twentieth objective of the invention that all of the integratable options be programmed in non-volatile memory at the time of instrument manufacture. It should be noted that the vast percentage of applications will be satisfied with relatively few combinations of voltage, LED color assignment, and transducer "class". Therefore, very high level subassemblies could be stocked waiting for programming information that transforms them into any of thousands of option combinations.
The possibilities of transducer calibration for, say, resistive senders is huge, when accounting for absolute value, offsets, linearity, and direction (increasing versus decreasing). However, these can be conveniently lumped into broad classes of absolute value, say, two or three broad classes. When this is done via resistor stuffing at the subassembly level, it becomes a simple matter to fine tune the absolute value, adjust the offset, resolve the linearity relative to the desired display response, and assign the direction in non-volatile programming at this essentially "functionally complete" level of assembly.
Further elaborating on this "one chip for all" theme, it is the intention in this design to optimize the low power consumption of the chip without compromising the high current drive capability, or the size (cost) of the chip. It is, therefore, the twenty first objective of the invention to operate at a low quiescent current, while maintaining high current drive capability.
There are two areas of absolute reference on-chip generation that require discussion. The first is the time base, and the second is the voltage reference. A very low cost, but moderately accurate time base is needed to establish all internal clocking, analog-to-digital conversion, LCD drive waveforms, display flashers, non-volatile memory loading, non-volatile memory viewing, etc. A fully integrated R-C oscillator operating at 131 kiloHerz (after trimming) followed by binary counting chains conveniently produces 64 Herz for the LCD drivers and 2 Herz for the flashers (divided by 2.sup.11 and divided by 2.sup.16, respectively). A low cost band gap voltage regulator can be created in CMOS with fair temperature coefficients and curvature error, but poor absolute value. With trimming, the regulator error can be brought into acceptable limits.
It is, therefore, a twenty second objective of the invention to integrate a small, low-cost oscillator and trim this oscillator with instructions from the non-volatile memory, with these instructions initially inserted during wafer test, but re-written during final assembly, if required.
It is, further, a twenty third objective of the invention to integrate an efficient, small, low-cost band gap regulator and trim the regulator with instructions from the non-volatile memory, with these instructions initially inserted during wafer test, but re-written during final assembly, if required.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.
This disclosure describes a display with ten (10) distinct states producing pointers, bar graphs, pictograms, icons, etc. The method can apply to any number of states, with 12, 15, 20, 25, etc., being quite practical. In every instance, the memorized thresholds will be one less than the number of display states. For example, 9 thresholds for 10 states and 24 thresholds for 25 states. It is, therefore, the twenty fourth objective of the invention to store in non-volatile, memory during the time of instrument manufacture a number of display states. Each of these thresholds will be stored digitally with a resolution commensurate with the desired accuracy and resolution of the analog-to-digital conversion process. It is, therefore, the twenty fifth objective of the invention to perform an analog-to-digital conversion process of sufficient accuracy and resolution to satisfy the stated instrument accuracy. Most often, the conversion process is expected to have resolutions of 6, 7, 8, 9, or 10 bits. This disclosure will focus on 8 bit examples, as they are quite appropriate for instrument applications in automotive and off-highway vehicles, motor/generator sets, motor/compressor sets, etc.